The present invention relates to the medical diagnostic and surgical arts. It finds particular application in conjunction with neurosurgery and will be described with particular respect thereto. It will be appreciated, however, that the invention finds application in conjunction with biopsies, endoscopic procedures, orthopedic surgeries, other medical procedures, industrial quality control procedures, and the like in which a tool or device must be accurately positioned in relation to an object.
Image guided surgery systems are particularly well adapted to intra-cranial and spinal surgery. These systems use diagnostic images of the patient to assist the physician with presurgical planning and to provide information relating to the position and orientation of the anatomy and instrumentation during a surgical procedure. Image guided surgery systems are a well-suited for use in connection with magnetic resonance ("MR") and computerized tomography ("CT") images, as well as with other imaging modalities.
In cranial applications, a patient reference frame may defined using three or more points fixed in relation to the patient's head. According to one method, at least three markers visible to the imaging device are affixed to the skin prior to imaging. According to another method, anatomical reference points are used. According to a third method, fiducial markers may be affixed to the skull, for example as disclosed in U.S. Pat. No. 4,991,579, Method and Apparatus for Providing Related Images of the Anatomy over time of a Portion of the Anatomy Using Fiducial Implants, to Allen, issued Feb. 12, 1991. Similar techniques may be used to define a patient reference frame with respect to other portions of the anatomy.
An image of the patient having an image reference frame is then obtained. Based on the location of the three or more markers within the image data, the image and patient reference frames can be correlated. Hence, the position of a feature of interest within the image can be determined with respect to the patient reference frame. After image acquisition is complete, the patient can be moved as desired. The patient is subsequently placed in an operating room environment, for example on an operating table.
The patient and operating room reference frames are correlated or "zeroed" by touching the surgical tool to the at least three markers. The position of the tool with respect to the cameras, and hence the position of the markers, is then determined. Inasmuch as the relationship between the patient, operating room, and image frames of reference is known, the position of the tool with respect to the image reference frame can then be determined. Relevant images, with the position of the surgical tool indicated thereon, are then displayed on a monitor. The surgeon is thus provided with a real time indication of the position of the surgical tool with respect to the previously obtained image.
Various surgical procedures require accurate placement of surgical tools in relation to the body. The accurate placement of these devices requires the determination of the trajectory and depth to the intended target. When the trajectory and depth information is determined, it is necessary to preserve that information, and then effectively use it for placement of the surgical device. One potential problem is that the orientation of the surgical device may intentionally or unintentionally change during placement of the device.
Hence, a surgical guide usable in connection with an image guided surgery system and which can be used to accurately place a surgical tool is needed. Such a device should allow the surgeon to readily determine the trajectory and position defined by the guide prior to the insertion of the tool. The guide should be unobtrusive, easy to use, and usable with a variety of surgical tools. Once a desired position has been determined, the guide should also be stable so as to reduce the likelihood of inadvertent changes in position.